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<p style="margin-top:0;margin-bottom:0">Thank you, I better understand the <span>behavior</span> of Thread_Init now.<br>
</p>
<p style="margin-top:0;margin-bottom:0">The issue with OpenMP is that one thread of the parallel part will be kept
<span>(the master thread) to execute the <span>remaining</span> lines. For this thread, a PPL::Thread_Init variable must not be deleted. This is why the integration with OpenMP require some additional line of code:
</span></p>
<p style="margin-top:0;margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0;margin-bottom:0"><span></p>
<div>#pragma omp parallel<br>
{<br>
PPL::Thread_Init *thread_init = NULL;<br>
bool thread_init_valid = true;<br>
#pragma omp master<br>
{<br>
thread_init_valid = false;<br>
}<br>
if(thread_init_valid)<br>
thread_init = new PPL::Thread_Init();</div>
<div><br>
#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
<i>PPL::C_Polyhedron ph1(3); <br>
PPL::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);</i><br>
}<br>
if(thread_init_valid)<br>
delete(thread_init);<br>
}</div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><i>PPL::C_Polyhedron ph3(3);</i></span> // ==> Ok (executed by the master thread)<br>
</div>
</span><br>
<p></p>
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<div>Regards,<br>
Thomas.</div>
<br>
<br>
<div style="color: rgb(0, 0, 0);">
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri, sans-serif"><b>De :</b> Enea Zaffanella <zaffanella.enea@gmail.com> de la part de Enea Zaffanella <zaffanella@cs.unipr.it><br>
<b>Envoyé :</b> jeudi 4 janvier 2018 14h53<br>
<b>À :</b> Thomas LE MÉZO<br>
<b>Cc :</b> The Parma Polyhedra Library developers' list<br>
<b>Objet :</b> Re: [PPL-devel] OpenMP & PPL</font>
<div> </div>
</div>
<div style="background-color:#FFFFFF"><br>
<div class="x_moz-cite-prefix">On 04/01/2018 11:30, Thomas LE MÉZO wrote:<br>
</div>
<blockquote type="cite">
<div id="x_divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, "EmojiFont", "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
<p style="margin-top:0; margin-bottom:0">I have found an issue with the use of Thread_Init object, the following code does not work:<br>
</p>
<p style="margin-top:0; margin-bottom:0"><i><br>
</i></p>
<p style="margin-top:0; margin-bottom:0"><span id="x_divtagdefaultwrapper" style="font-size:12pt"></span></p>
<div><i>#pragma omp parallel</i></div>
<div><i>{</i></div>
<div><i> PPL::Thread_Init thread_init;<br>
</i></div>
<div><i>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
PPL::C_Polyhedron ph1(3); <br>
PPL::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</i></div>
<div><i>}</i></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><i>PPL::C_Polyhedron ph3(3); // => Segment fault</i></span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><br>
</span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt">It seems that when all the thread_init variables are delete, it is then impossible to instantiate or proceed to any operation with ppl.</span></div>
</div>
</blockquote>
<br>
That is the expected behavior.<br>
Each thread willing to call the PPL (even the master thread) should first call the thread initialization code.<br>
<br>
<blockquote type="cite">
<div id="x_divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, "EmojiFont", "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt">A workaround is to instantiate a new Thread_Init variable but this is a bit heavy.</span></div>
</div>
</blockquote>
<br>
I can't see why this is "heavy".<br>
Note: you can place the thread initialization code for the master thread in the main function.<br>
The thread will be initialized once at program start and finalized when exiting the program.<br>
<br>
Regards,<br>
Enea.<br>
<br>
<blockquote type="cite">
<div id="x_divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, "EmojiFont", "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"></span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><span id="x_divtagdefaultwrapper" style="font-size:12pt">
<div><i>#pragma omp parallel</i></div>
<div><i>{</i></div>
<div><i> PPL::Thread_Init thread_init;<br>
</i></div>
<div><i>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
PPL::C_Polyhedron ph1(3); <br>
PPL::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</i></div>
<div><i>}</i></div>
<div><i><span id="x_divtagdefaultwrapper" style="font-size:12pt"><span id="x_divtagdefaultwrapper" style="font-size:12pt"><span id="x_divtagdefaultwrapper" style="font-size:12pt">PPL::Thread_Init thread_init;</span></span></span><br>
</i></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><i>PPL::C_Polyhedron ph3(3); // => OK</i></span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><br>
</span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt">Any other idea?</span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt"><br>
</span></div>
<div><span id="x_divtagdefaultwrapper" style="font-size:12pt">Thomas</span><span id="x_divtagdefaultwrapper" style="font-size:12pt"></span><br>
<span id="x_divtagdefaultwrapper" style="font-size:12pt"></span></div>
</span></span></div>
<br>
</div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri, sans-serif"><b>De :</b> Thomas LE MÉZO<br>
<b>Envoyé :</b> mercredi 3 janvier 2018 12:26:09<br>
<b>À :</b> <a class="x_moz-txt-link-abbreviated" href="mailto:enea.zaffanella@unipr.it">
enea.zaffanella@unipr.it</a><br>
<b>Cc :</b> The Parma Polyhedra Library developers' list<br>
<b>Objet :</b> RE: [PPL-devel] OpenMP & PPL</font>
<div> </div>
</div>
<div dir="ltr">
<div id="x_x_divtagdefaultwrapper" dir="ltr" style="font-size: 12pt; color: rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif, "EmojiFont", "Apple Color Emoji", "Segoe UI Emoji", NotoColorEmoji, "Segoe UI Symbol", "Android Emoji", EmojiSymbols;">
<p style="margin-top:0; margin-bottom:0">It seems to work! To avoid multiple instantiation of
<span>thread_init</span>, a solution is to break down the "omp parallel for" in two lines:<br>
</p>
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<div>#pragma omp parallel</div>
<div>{</div>
<div><span> PPL::Thread_Init thread_init;</span><br>
</div>
<div>#pragma omp for<br>
for(int i=0; i<1000; i++){<br>
<span><span>PPL</span></span>::C_Polyhedron ph1(3); <span></span><br>
<span><span>PPL</span></span>::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</div>
<div>}<br>
</div>
<br>
<div id="x_x_divtagdefaultwrapper" dir="ltr" style="">Thank you very much,</div>
<div dir="ltr" style="">Thomas<br>
<br>
<br>
<div style="color:rgb(0,0,0)">
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_x_divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" color="#000000" face="Calibri,
sans-serif"><b>De :</b> Enea Zaffanella
<a class="x_moz-txt-link-rfc2396E" href="mailto:zaffanella.enea@gmail.com"><zaffanella.enea@gmail.com></a> de la part de Enea Zaffanella
<a class="x_moz-txt-link-rfc2396E" href="mailto:zaffanella@cs.unipr.it"><zaffanella@cs.unipr.it></a><br>
<b>Envoyé :</b> mercredi 3 janvier 2018 11h17<br>
<b>À :</b> The Parma Polyhedra Library developers' list; Thomas LE MÉZO<br>
<b>Objet :</b> Re: [PPL-devel] OpenMP & PPL</font>
<div> </div>
</div>
<div style="background-color:#FFFFFF">
<p><br>
</p>
<br>
<div class="x_x_x_moz-cite-prefix">On 31/12/2017 17:33, Thomas LE MÉZO wrote:<br>
</div>
<blockquote type="cite">
<div id="x_x_x_divtagdefaultwrapper" dir="ltr" style="">
<p style="margin-top:0; margin-bottom:0">Dear <span>Enea, Dear all,</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span>I tried recently to implement a multi-thread version of my thesis code using PPL library. I used OpenMP and the last version of ppl on devel git branch as I read you have been working on a thread-safe implementation
(thread-safe option with configure). I didn't succeed in writing a correct program; see for instance this simple code that return a segmentation fault :</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>#include <omp.h></span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>namespace PPL = Parma_Polyhedra_Library;</span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span><span>int main(){</span><br>
</span></p>
<p style="margin-top:0; margin-bottom:0"><span></span></p>
<div>#pragma omp parallel for<br>
for(int i=0; i<1000; i++){<br>
<span><span>PPL</span></span>::C_Polyhedron ph1(3); // => segmentation fault
<span>at line 83 of Linear_Expression.cc</span><br>
<span><span>PPL</span></span>::C_Polyhedron ph2(3);<br>
ph1.intersection_assign(ph2);<br>
}</div>
<div> return 0;</div>
<div>}<br>
</div>
<br>
<p style="margin-top:0; margin-bottom:0">Would you have any idea about what is wrong?</p>
</div>
</blockquote>
<br>
Each thread should be properly initialized by creating a PPL::Thread_Init object (and finalized by destroying it).<br>
See for instance test01() in tests/Polyhedron/threadsafe1.cc<br>
As an alternative, you could use the make_threadable wrapper (see test02() in the same test).<br>
<br>
<blockquote type="cite">
<div id="x_x_x_divtagdefaultwrapper" dir="ltr" style="">
<p style="margin-top:0; margin-bottom:0">Is PPL compatible with using OpenMP?</p>
</div>
</blockquote>
<br>
I never tried using it with OpenMP ... however, as long as thread initializations (and finalizations) are performed as suggested above, things should be working (there is also a library initialization part, but that is automatically done when working in C++).<br>
<br>
In you code, I would try adding<br>
<br>
PPL::Thread_Init thread_init;<br>
<br>
as the very first line of the loop body.<br>
This would maybe create more init objects than needed,<br>
but (if I remember correctly) that should not be a problem.<br>
<br>
Let us know how it goes.<br>
<br>
Enea<br>
<br>
<blockquote type="cite">
<div id="x_x_x_divtagdefaultwrapper" dir="ltr" style="">
<p style="margin-top:0; margin-bottom:0"><br>
</p>
<p style="margin-top:0; margin-bottom:0">Thanks a lot in advance,</p>
<p style="margin-top:0; margin-bottom:0">Thomas<br>
</p>
<br>
</div>
<br>
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